Method for Detecting and Classifying Block Edge from Dct-Compressed Image

1. A method for detecting and classifying block edges from DCT (Discrete Cosine Transform)-compressed images, the method comprising: (a) extracting DCT coefficients by N×N blocks constituting a compressed image; (a1) forming a plurality of regions in each block, each region defining a direction; and (b) applying an arithmetic operation defined for each direction to the DCT coefficients obtained in (a), and comparing results of the arithmetic operations among the directions of a corresponding block to determine an edge direction component for the corresponding block, the arithmetic operations using an averaged luminance value of each region represented in terms of the DCT coefficients.

2. The method as claimed in claim 1 , wherein the arithmetic operation of (b) comprises a combination of H, V, and D that are the weighted sums of the extracted DCT coefficients as given by the following equations: H = ∑ n = 1 N - 1 ( odd ) ⁢ w ⁡ ( 0 , n ) ⁢ X ⁡ ( 0 , n ) V = ∑ n = 1 N - 1 ( odd ) ⁢ w ⁡ ( m , 0 ) ⁢ X ⁡ ( m , 0 ) D = ∑ n = 1 N - 1 ( odd ) ⁢ w ⁡ ( n , n ) ⁢ X ⁡ ( n , n ) + ∑ m = 1 N - 1 ( odd ) ⁢ ∑ n = 1 m - 1 ( odd ) ⁢ w ⁡ ( m , n ) ⁢ ( X ⁡ ( m , n ) + X ⁡ ( n , m ) ) where m and n represent spatial frequency components in vertical and horizontal directions, respectively, and satisfy 0≦m, n≦N.

3. The method as claimed in claim 1 , wherein (a) comprises extracting Y(m, n)=w(m, n)X(m, n) that is a multiplication of the DCT coefficient X(m, n) by a quantitative numeric, rather than simply extracting the DCT coefficient, wherein (b) of performing each arithmetic operation comprises determining H, V, and D according to the following equations to construct an arithmetic operation for each direction using a combination of H, V, and D: H = ∑ n = 1 N - 1 ( odd ) ⁢ Y ⁡ ( 0 , n ) , ⁢ V = ∑ n = 1 N - 1 ( odd ) ⁢ Y ⁡ ( m , 0 ) , ⁢ D = ∑ m = 1 N - 1 ( odd ) ⁢ ∑ n = 1 N - 1 ( odd ) ⁢ Y ⁡ ( m , n ) ⁢ .

4. The method as claimed in claim 2 , wherein (b) of calculating H, V, and D comprises performing summations up to upper limits of the “m” and “n” set to L (1≦L≦N−1) rather than N−1 to construct the arithmetic operation for each direction.

5. The method as claimed in claim 3 , wherein (b) of calculating H, V, and D comprises performing summations up to upper limits of the “m” and “n” set to L (1≦L≦N−1) rather than N−1 to construct the arithmetic operation for each direction.

6. The method as claimed in claim 4 , wherein (b) comprises setting L=1, and computing H, V, and D with w(0,1)=w(1,0)=w(1,1)≈0.5 α.